The Justice Department just got a new boss: Jeff Sessions. He is raising alarms in the civil rights community. The Leadership Conference on Civil and Human Rights is concerned about his “record of hostility” toward the Voting Rights Act and the enforcement of civil rights. The NAACP-Legal Defense Fund lamented that it is “unimaginable that he could be entrusted to serve as the chief law enforcement officer for this nation’s civil rights laws.” No one knows for sure how Sessions will perform as attorney general — the former Republican senator from Alabama did, after all, once vote to renew the Voting Rights Act, in 2006 — but for many his record is deeply troubling.

Voter identification laws have spread rapidly in the past 10 years

What we do know is that voter identification laws are spreading rapidly around the country. Before 2006, no state required photo identification to vote on Election Day. Today 10 states have this requirement. All told, a total of 33 states — representing more than half the nation’s population — have some version of voter identification rules on the books.

As we detail below, our research shows that these laws lower minority turnout and benefit the Republican Party.

There is, of course, widespread debate about the merits of these new laws. Proponents claim that ID laws are necessary to reduce fraud and to restore trust in the democratic system. Critics claim that voter ID laws serve as effective barriers that limit the legitimate participation of racial and ethnic minorities and other disadvantaged groups.

This year more states than ever will require potential voters to show photo ID in order to vote in the election. Here's why this is so controversial. (Monica Akhtar/The Washington Post)

Who is right? Scholars have been able to show that racial and ethnic minorities have less access to photo IDs, and extensive analysis reveals almost no evidence of voter fraud of the type ostensibly prevented by these laws. But determining just how many Americans are prevented from actually voting is another question altogether. The key question is not whether there could be worrisome effects from these laws, but whether clear-cut shifts in electoral participation and outcomes have actually occurred. Do voter identification laws skew the electorate in favor of one set of interests over others?

Because these laws are so new, it has been almost impossible to assess their consequences. Most of the existing studies have looked at the effects of not-so-strict ID laws or have assessed the consequences of strict ID laws in only one state or one election. The results have been mixed.

Here’s how we did our research

In our new study we are able to offer a more definitive assessment for several reasons.

First and most important, we have data from the nation’s most recent elections (2006-2014) and can single out and test the effect of the strict voter ID laws in multiple elections and multiple states. (We define states with “strict voter ID laws” as states where residents cannot vote without presenting valid identification during or after the voting process.)

Second, we have validated voting data so we know whether each of our respondents actually voted. Third, we have a huge sample — over a third of a million Americans from the Cooperative Congressional Election Study — which means that we can analyze the participation of racial and ethnic minorities in all states both before and after strict ID laws are implemented.

When we compare overall turnout in states with strict ID laws to turnout in states without these laws, we find no significant difference. That pattern matches with most existing studies. But when we dig deeper and look specifically at racial and ethnic minority turnout, we see a significant drop in minority participation when and where these laws are implemented.

Hispanics are affected the most: Turnout is 7.1 percentage points lower in general elections and 5.3 points lower in primaries in strict ID states than it is in other states. Strict ID laws mean lower African American, Asian American and multiracial American turnout as well. White turnout is largely unaffected.

These laws have a disproportionate effect on minorities, which is exactly what you would expect given that members of racial and ethnic minorities are less apt to have valid photo ID.

In the graph below, we display the turnout gap between whites and Latinos, Asian Americans and African Americans in states with and without strict voter ID laws. In general elections in non-strict states, for instance, the gap between white and Latino turnout is on average 4.9 points.

But in states with strict ID laws, that gap grows to a substantial 13.2 points. The gap between white turnout and Asian American and African American turnout also increases.

The right side of the figure shows that the same thing happens in primary elections — and more dramatically. For example, the white-black turnout gap grows from 2.5 to 11.6 when a state adds strict ID laws. The racial imbalance in U.S. voting expands.

These findings persist even when we take many other factors into account — including partisanship, demographic characteristics, election contexts and other state laws that encourage or discourage participation. Racial gaps persist even when we limit our analysis to Democrats or track shifts in turnout in the first election after strict rules are implemented. Definitively determining that the laws themselves are what lowers turnout is always difficult without an experiment, but however we look at it, strict voter ID laws suppress minority votes.

When a state has strict voter ID laws, those who do vote are more conservative

All of this, of course, has real political consequences. Because minority voters tend to be Democrats, strict voter ID laws tilt the primary electorate dramatically.

All else equal, when strict ID laws are instituted, the turnout gap between Republicans and Democrats in primary contests more than doubles from 4.3 points to 9.8 points. Likewise, the turnout gap between conservative and liberal voters more than doubles from 7.7 to 20.4 points.

By instituting strict voter ID laws, states can alter the electorate and shift outcomes toward those on the right. Where these laws are enacted, the influence of Democrats and liberals wanes and the power of Republicans grows. Unsurprisingly, these strict ID laws are passed almost exclusively by Republican legislatures.

Sessions has opposed core elements of the Voting Rights Act and other measures aimed at protect minority voting rights. Perhaps strong evidence that voter identification reduces minority voting will change his mind in this case.

We will know soon; the Justice Department’s case against Texas’s strict voter ID law will resume after a month-long delay requested by the new Trump-led department. Sessions will have to decide whether to continue the case.

Zoltan Hajnal is professor of political science at the University of California at San Diego.

Nazita Lajevardi is assistant professor of political science at Michigan State University.